1. Field of the Invention
The present invention relates to an X-ray generation apparatus, specifically, one which makes it possible to generate high X-ray output by use of a smaller apparatus than the conventional size.
The ordinary method, which generates X-ray using irradiation of accelerated electrons to a target, adapted an X-ray generation apparatus. However, when electrons, which are accelerated by some tens of thousands voltage, collide with the target, only 1% of the accelerated electron energy changes to X-ray energy and the remaining 99% is consumed by Joule's heat. It is essential to investigate how to effectively radiate one hundred times the thermal energy incidental to X-ray generation from the target, in order to obtain a high output X-ray generation apparatus. The range of X-ray strength generated by an apparatus depends on the target material and cooling ability. The generated X-ray energy can be increased by increasing electron irradiation energy within a range of the target not melted by irradiation of accelerated electrons.
Therefore, metal materials which have high thermal conductivity and high melting temperature are mainly used as the X-ray target, and the thermal energy is radiated by water cooling. Furthermore, in order to obtain high strength X-rays, a method by which the target is cooled while rotating has been developed. In this method, a portion of the target which is irradiated by electrons and emits X-rays, rotates one after another, the temperature of the target does not increase, and higher X-ray energy can be obtained compared with a fixed type target.
2. Description of the Prior Art
A diamond containing target, in which the diamond is embedded in a copper substrate by powder sintering, is used and the target is cooled and rotated in an X-ray generation apparatus shown in Tokkai-Sho 57 (1982)-38548. However, it has been pointed out that as the size of such X-ray apparatus increases, it is imperative to prevent vibration when rotating the target. Furthermore, there are problems with decreased efficiency of the electron beam when the electron beam irradiates both copper and diamond.
An X-ray generation apparatus, in which an electron beam irradiates in the direction of a heat resistant single crystal axis, emits X-rays in the direction of the single crystal axis and a cooling means of the single crystal is prepared, as shown in Tokkai-Hei 2 (1990)-309596. However, there are arguments that the target is cooled insufficiently because the electron irradiating portion of the target is cooled through the peripheral portion of the single crystal.
An anticathode for X-ray generation which is made from a 2-layer structure of high heat conductive inorganic material and thin metal film, is shown in Tokkai-Hei 5 (1993)-343193. Effective cooling is expected when the back portion of the high heat conductive inorganic material is cooled as shown in this prior art. However, when the target is adapted for an X-ray generation apparatus and is cooled at the peripheral portion (as shown in Tokkai-Hei 2-309596), the target does not have sufficient cooling ability because a considerable amount of thermal energy diffuses along the thin metal film for which heat conduction is rather high. The other problem is exfoliation of the thin metal film. A method of synthesizing diamond from the gaseous phase is disclosed in U.S. Pat. No. 4,767,608 issued Aug. 30, 1988, and in U.S. Pat. No. 4,434,188 issued Feb 28, 1994.